Exam 29: Magnetic Fields Due to Currents

Two parallel wires, 4 cm apart, carry currents of 2 A and 4 A respectively, in opposite directions. The force per unit length in N/m of one wire on the other is:

A long straight cylindrical shell has an inner radius R_i and an outer radius R_o. It carries a current i, uniformly distributed over its cross section. A wire is parallel to the cylinder axis, in the hollow region (r < R_i). The magnetic field is zero everywhere outside the shell (r > R_o). We conclude that the wire:

A toroid has a square cross section with the length of an edge equal to the radius of the inner surface. The ratio of the magnitude of the magnetic field at the inner surface to the magnitude of the field at the outer surface is:

A wire carrying a large current i from east to west is placed over an ordinary magnetic compass. The end of the compass needle marked "N" will point:

The magnitude of the magnetic field at point P, at the center of the semicircle shown, is given by:

Two long straight wires enter a room through a window. One carries a current of 3.0 A into the room while the other carries a current of 5.0 A out. The magnitude in T.m of the path integral around the window frame is:

Helmholtz coils are commonly used in the laboratory because the magnetic field between them:

The diagram shows three equally spaced wires that are perpendicular to the page. The currents are all equal, two being out of the page and one being into the page. Rank the wires according to the magnitudes of the magnetic forces on them, from least to greatest.

Two long straight wires are parallel and carry current in opposite directions. The currents are 8.0 A and 12 A and the wires are separated by 0.40 cm. The magnetic field in tesla at a point midway between the wires is:

If the radius of a pair of Helmholtz coils is R then the distance between the coils is:

The magnetic field a distance 2 cm from a long straight current-carrying wire is 2*10^-5 T. The current in the wire is:

Which graph correctly gives the magnitude of the magnetic field outside an infinitely long straight current-carrying wire as a function of the distance r from the wire?

Two long ideal solenoids (with radii 20 mm and 30 mm respectively) carry the have the same number of turnes of wire per unit length. The smaller solenoid is mounted inside the larger, along a common axis. It is observed that there is zero magnetic field within the inner solenoid is zero. The current in the inner solenoid must be:

Two long parallel straight wires carry equal currents in opposite directions. At a point midway between the wires, the magnetic field they produce is:

In Ampere's law, the symbol is:

The magnetic field at any point is given by where is the position vector of the point and A is a constant. The net current through a circle of radius R, in the xy plane and centered at the origin is given by:

In the figure, the current element the point P, and the three vectors (1, 2, 3) are all in the plane of the page. The direction of due to this current element, at the point P is:

Solenoid 2 has twice the radius and six times the number of turns per unit length as solenoid 1. The ratio of the magnetic field in the interior of 2 to that in the interior of 1 is:

A toroid with a square cross section carries current i. The magnetic field has its largest magnitude:

A "coulomb" is: